The present disclosure relates to a gas turbine engine and, more particularly, to a fuel injector system therefor and method of operation.
Gas turbine engines, such as those that power modern commercial and military aircraft, include a compressor section to pressurize a supply of air, a combustor section to burn a hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases and generate thrust.
The combustor section generally includes a plurality of circumferentially distributed fuel injectors that axially project into a combustion chamber to supply fuel to be mixed with the pressurized air. Gas turbine engines typically include plurality individually controlled centralized staging valves with plurality fuel supply manifolds that deliver fuel to the fuel injectors. There is one fuel supply manifold for each stage, thus, each fuel injector may have plurality fuel supply connections, one for each stage.
Each fuel injector typically has an inlet fitting connected to the manifold at the base, a conduit or stem connected to the base fitting, and a nozzle tip assembly connected to the conduit or stem to spray the fuel into the combustion chamber. Appropriate valves and/or flow dividers are provided to direct and control the flow of fuel through the nozzle assembly.
The nozzle assembly often includes pilot and main nozzles. Generally, the main nozzles are for normal and high power situations, while the pilot nozzles are used for start operation. The nozzles have relatively small openings and fuel passages in the conduit that may be prone to coke formation due to high fuel temperature. Coke formation may result in narrowed fuel openings, uneven fuel burn and increased maintenance requirements. Further, coke formation may form in the fuel conduit of the fuel injector, break off in fragments and ultimately obstruct fuel injector nozzle tip openings.
Conventional fuel injector designs typically utilize heat shields around the fuel injector conduit to provide an insulated, static, air gap and reduce the heat transfer rate within the diffuser case module to the fuel. With ever increasing diffuser case air temperatures in current and future engines and where fuel is utilized to cool auxiliary systems prior to entering a fuel injector system of the engine, improved means to reduce fuel heating rates through the fuel injector conduit, and thereby minimize coking, is desirable.